Plastic insulated bayonet base



Aug. 30, 1955 A. c. SZAFRAN ET AL PLASTIC INSULATED BAYONET BASE lnven korsz AdoLph C. SzarFvan,

A t torneg.

Robert L.Imboden,

Their Filed Feb. 7, 1951 United States PatentUfilice 2,716,742 Patented Aug. 30, 1955 PLASTIC INSULATED BAYoNET BASE Adolph C. Szafran, Euclid, and'Robert L. Imboden, Lyndhurst, Ohio, assignors to General Electric Company, a corporation of New York; patent dedicated to the Public insofar as it relates to lamps and lamp parts to the extent stated in document recorded'in the United States Patent Oifice, January 4, 1954, Liber U-238,' page 394 Application February 7, 1951, Serial=No. 209,738

7 Claims. (Cl. 339145) This invention relates to bases for electrical devices, and particularly to multiple contact bases for electric lamps as exemplified in'the common two contact bayonet type base.

The bases of electric lamps are generally fabricated as units apart from the bulbs. Such a base-comprises an external metal shell provided with means for locking it in a socket, and one or more end contact terminals which are secured to the body of the shell by a 'b'utton or web of insulating'material. Tocomplete a lamp, a base unit is mounted and cemented fast aroundthe" scaled neck of a lamp bulb, and lead in wiresfrom the bulb are connected to the contacts of the base by soldering or welding.

The invention herein is particularly concerned with the type of base known as a bayonet base wherein the metal shell is equipped with radial pins for'securing it in a socket. With this type of base, the shell itself may or may not be used as" a contact terminal for the base. Where the shell is used as a contact terminal, only one bottom contact need be provided at the end' of the shell to permit a circuit to the filament within the bulb. Where the shell is not used as a terminal, it is' necessary to provide at least two bottom'contacts at the end of the shell. Likewise, where a plurality of filaments are provided which are to be controlled separately, it is necessary to provide more than one end contact, even though the shell itself is used as'a-terminal.

The general practice in the incandescent lamp industry up to the present time has' been to secure'the contacts to the shell by means of a button or web of glass. The glass must be molded'in at a relatively high temperature, and this has necessitated theme of a metal for the shell which can resist these high temperatures, for instance, brass. However, due to economic reasons, it is becoming increasingly desirable to substitute cheaper and more available metals for the brass. Aluminum is such-a metal, but it cannot withstand the high temperatures required for molding the glass web. Consequently, an insulating material having a lower fusion or molding temperature must be utilized for the web to secure the contacts. Among such materials which hold forth considerable promise, may be mentioned the thermosetting plastics such as phenol, urea or melamine formaldehyde. These plastics require much higher molding pressures than glass, and a new set of problems is encountered'in attempting to use them in a lamp base.

Accordingly, it is an object of the present invention to provide a new and improved lamp basic structure permitting the use of a high-pressure'molding compound in a base having a plurality of-'bottomcontacts.

Another object of the invention is to' provide a" new and improved multiple contact bayonet typ'e lam'p base wherein'the web is composed of a plastic material molded at a high pressure.

The specific object of the invention is to provide an improved bayonet-type 1 two=contact lamp base wherein the bottom contacts are mounted on individual raised bosses in a web of thermosetting plastic requiring a high molding pressure.

One of the most troublesome problems in the molding of high pressure plastics is that of keeping the surfaces of inserts free of flash, that is, free of a thin running over of the plastic. For instance, in the case of a lamp base, it is essential that the bottom contacts or eyelets be completely exposed and free from flash in order that electrical contact will be made to the lamp when it is inserted in a socket. In accordance with the invention, the solution to this problem has been found in mounting each contact or eyelet on its own individual boss, the boss being so dimensioned that its diameter, at the point where the eyelet covers it, is only very slightly larger than the diameter of the eyelet. In order to facilitate insertion of the lamp into its socket, it is necessary to provide means to depress or cam the spring contacts of the socket. Wth the usual bayonet type socket, the lamp must be rotated in the socket a fraction of a turn in order for the radial pins of the base to lock in the slots provided for that purpose. In accordance with our invention, such rotation is made possible by providing, in the plastic web, cam surfaces or projections leading onto the bosses on which the eyelets are mounted, these cam surfaces being at the same level as the lower or outer surface of the eyelets.

For further objects and adavantages and for a better understanding of the invention, attention is now directed to the following description and accompanying drawing. The features of the invention believed to be novel will bemore particularly pointed out in the appended claims.

In the drawing:

Fig. l is a pictorial view of a well-known type of miniature lamp provided with a two-contact bayonet-type base embodying our invention, and of a socket positioned for receiving the lamp.

Fig. 2 is an end view of a base comprising a molded thermosetting plastic insulating web and embodying our invention.

Figs. 3 and 4 are transverse sectional views of the base illustrated in Fig. 2 and taken along the section planes IIIIII and IVIV, respectively.

Fig. 5 is a cross sectional view of a mold and its associated force or plunger for molding a plastic insulation web onto a shell with the eyelets properly located at the bottom thereof to make a lamp base in accordance with the invention.

Referring to Fig. 1, there is shown a miniature incandescent lamp which, except for its base, is similar to well known types widely used commercially. The lamp 1 comprises a glass bulb 2 evacuated of air and preferably filled with an inert gas and containing a pair of filaments 3 and 3' mounted on lead-in wires 4 which project out through a glass press 5. The lower end of the bulb is constricted or reduced in diameter below the line where it is cemented to a base 6. The base comprises a cylindrical metal shell 7 having one end open for accommodating the bulb 2. The shell is provided with means allowing indexing thereof in a socket and comprising a pair of radial projecting pins 8 and 9 on its lateral surface. These pins are for the purpose of engaging notches at the bottom of slots in a socket into which the lamp is to be inserted. A pair of bottom contacts in the form of eyelets l0 and 11 are located in an insulating web 12 at the lower end of the shell 7. These bottom contacts serve as terminals for two of the lead-in wires 4 which are soldered to them. In the lamp illustrated, it is usually desirable to be able to control both filaments independently. Accordingly, the shell 7 itself used as one terminal which is common to one side of each filament, and the bottom'contacts 1t) and 11, which are connected through the lead-in wires to the other side of the filaments,

permit connecting one filament into a circuit without the other.

A well-known-form of socket is shown at 13 in the position which it would occupy for receiving a lamp. The socket comprises a metal shell 14 having an inside diameter slightly greater than the outside diameter of the shell 7 of the base of the lamp. The shell 14 is longitudinarly slotted at 15 and 16 on opposite sides in order to receive the radial pins 3 and 9 when the lamp is inserted. The slots are continued at the bottom into circumferentially displaced upwardly facing notches, as may be seen at 16 in connection with slot 16. The lamp is locked into the socket by rotating it a fraction of a turn after it has been pushed in so that the radial pins enter the corresponding notches in the longitudinal slots. The socket comprises a plunger type disc or insulating washer 17 in whose upper surface are located a air of slightly raised eyelet type terminals and 19 which are adapted to coact with the bottom contacts 19 and 11 of the base when the lamp is inserted into the socket. The disc 17 is forced upwards by means of a spiral spring 20 which is compressed between it and the inwardly flanged lower edge of the shell 14. The upward force which the terminals 18 and 19 exert on the bottom contacts of the lamp locks the radial pins 3 and 9 in the notches of the radial slots so that the lamp is held securely in the socket. The electrical connections to the filaments are made through the wires 21 which are connected to the metal shell 14 and to the terminals 18 and 19.

By reason of the method whereby the lamp is inserted into the socket and rotated a fraction of a turn during the process, it will be understood that the lower surfaces of the contacts and 11 must be approximately flush with the adjoining surface of the web 12 against which the terminals 13 and 19 initially make contact. This is all the more necessary with other types of sockets wherein the terminals 13 and 19 are separately spring loaded. According to the prior art, the practice has been to make the lower surface of the web 12 flat and to mount the eyelets flush upon it. This is the construction which has been commonly employed where the insulating web is made of glass.

In making lamp bases wherein the bottom contacts or eyelets are mounted flush on the lower surface of the glass web, it has been the practice to locate the eyelets in the mold by placing them on pins. During the molding operation, there may be a tendency for a force or plunger to force a. small uantity of into the holes through the eyelets. However, since a relatively low pressure is utilized for molding the glass, the amount of glass forced into the holes is usually insignificant and easily cleaned out, so that there is no difiiculty in soldering the lead-in wires to the eyelets.

When the prior art dies and molding process are utilized with a high pressure molding plastic, it is found that the plastic material packs tightly between the locating pins and the inner wall of the hole through the eyelet. There is also a tendency for flash to form on the lower surface of the eyelets so that a secondary operation is required to remove it in order to permit soldering of the lead-in wires. As a result, it has been found uneconomical to utilize the prior art type of mold and configuration of the plastic web.

Our invention eliminates the need for pins to locate the eyelets within the mold and requires only one molding operation because practically no flash occurs on the lower surfaces of the eyelets. In accordance with our invention, the contact eyelets 10 and 11 are mounted on raised projections or primary bosses 22 and 23 displaced from the center of the web. This permits placing the eyelets in suitable recesses or nests within the molding cavity so that no locating pins are needed to hold them in place during the molding process. The elimination of the locating pins in the mold permits the provision of plunging pins on the lower surface til of the force. These pins enter holes through the eyelets during the molding operation and prevent any plastic material from adhering to the inner surfaces of the hole through the eyelets. Moreover, the plunging pins are designed to form lead holes, through the insulation, smooth enough to permit automatic threading of lead-in wires.

In order to permit rotation of the base after its insertion in the socket so as to lock the radial pins in their cooperating notches, the primary or eyelet mounting bosses 22 and 23 have secondary bosses or raised portions 24 and 25, respectively, appended to them and joining them on one side. The plan configuration of the bosses may be seen more readily in Fig. 2, and it will be observed that the secondary bosses extend laterally from the primary bosses along a generally arcuate path. These secondary bosses may be considered as functional bottom surfaces retained from a conventional glass web. They are necessary in order to cam or, in other words, to depress the contacts of the socket when the lamp is inserted within it. The connecting portions between the secondary bosses 24 and 25 and the corresponding primary bosses 22 and 23 are preferably narrow, with the result that the secondary bosses have a tear-shaped outline. The primary reason for this configuration is in order to have as narrow a cross section as possible where the plastic material is flush with the eyelets and abuts against it. The opportunity for the formation of flash, that is, running over of plastic on the exposed surface of the eyelet, is thus reduced. The secondary and fairly obvious reason for the configuration which has been illustrated is in order to save the quantity of plastic which would otherwise be required to fill in the recessed portions of the web.

Fig. 3 shows a cross-sectional View of the base through the plane III-III with reference to Fig. 2, and illustrates the internal disposition of the plastic material as a result of the molding operation. It will be observed that the inner configuration of the plastic is such that the inward projections of the radial pins 8 and 9 are embedded and locked in it. Fig. 4, which is a crosssectional view of the base through the plane IV-IV illustrates the manner in which the eyelets are fastened on the bottom surfaces of the primary bosses by means of inwardly turned flanges at 26 and 27.

Referring to Fig. 5, there is shown in cross-sectional outline a fragment of a mold 30 and its associated plunger 31, more commonly referred to as a force, for making a lamp base in accordance with the invention. The mold 30 is hollowed out into a cylindrical cavity of a diameter to permit the shell 7 to fit snugly within it and yet large enough to enable it to be readily removed after the molding operation. The lower face of the cylindrical cavity is shaped to the contour of the lower face of the web as illustrated in the preceding figures of the drawing. The nest or recess at 32 has a diameter just slightly larger than the eyelet 10 which is placed in it preparatory to the molding operation, leaving a small clearance between the eyelet and the edge of the recess. The recess 32 is also provided with a central hole 33 through which any plastic entering the bore of the eyelet 10 may be forced out. A predetermined quantity of plastic material of the thermosetting type such as phenol formaldehyde is placed within the mold as shown at 34. The force or plunger 31 is adapted to descend into the shell 7 and to compress the plastic material. A pair of plunger pins, of which 35 is illustrated in the figure, are fitted into the lower face of the force and are adapted to enter the plastic material and also the bore through the eyelet 10 so as to form a lead-in hole; the plunger pins keep the bore of the eyelet free of plastic material that might enter it by forcing such material out through the hole 33.

In the molding operation, the force moves down and applies a pressure in the range of a few thousand pounds per square inch to the plastic material. The mold is also heated by suitable means, not shown in the drawing, to the required temperature for effecting the cure or polymerization of the plastic material, usually in the neighborhood of 350 F. If desired, a preform, that is, a predetermined quantity of plastic material compacted together may be utilized instead of the loose plastic material which has been illustrated in the drawing. As the force descends, the plunger pins enter the eyelet holes and move down into the holes 33 in the cavity. These pins form the smooth surfaced lead-in holes and keep the eyelet holes free from flash. As the plastic is compressed and begins to flow, it fills the mold and presses the eyelets tightly into their nests and holds them in place. Some plastic flows into the very small clearance space between the edges of the eyelets and the vertical walls of the nests. in these very thin sections, the heat from the mold quickly penetrates throughout the plastic so that it cures or polymerizes rapidly and freezes the flow, thereby preventing any of it from passing under the eyelets and preventing the formation of objectionable flash. This feature is more fully described and is claimed in the copending application No. 209,816, filed February 7, 1951, of Albert P. Pate and Robert L. lmboden, entitled Plastic insulated Lamp Base and assigned to the same assignee as the present invention.

While a certain specific embodiment has been shown and described, it will of course be understood that various modifications may be made without departing from the invention. Thus, whereas the invention has been illustrated with respect to a bayonet-type, two-contact base, it is equally applicable to other bases having a plurality of bottom contacts Where flush camming surfaces are required in contiguous relation to the contact surfaces. The appended claims are therefore intended to cover any such modifications coming within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A base for electrical devices comprising a cylindrical shell, means on said shell for indexing said base in a socket, a plastic web closing the bottom end thereof, primary bosses projecting from the outer surface of said web and displaced from the center thereof, electrical contacts mounted and exposed on the outer surfaces of said primary bosses, and secondary bosses projecting from said web and abutting against said primary bosses and extending laterally therefrom along a generally arcuate path.

2. A base for electrical devices comprising a cylindrical metal shell, means on said shell for indexing said base in a socket, a plastic web closing the bottom end thereof, primary bosses projecting from the outer surface of said web and displaced from the center thereof, electrical contacts mounted and exposed on the outer surfaces of said primary bosses, and secondary bosses projecting from said web and abutting against said primary bosses and extending laterally therefrom along a generally arcuate path with their outer surfaces substantially flush with said contacts.

3. A plural end contact bayonet type base for electric lamps comprising a cylindrical metal shell, means on said shell for indexing said base in a socket, a plastic web closing the bottom end thereof, primary bosses projecting from the outer surface of said web and displaced from the center thereof, contacts mounted and exposed on the outer surfaces of said primary bosses, and secondary bosses projecting from said web and having constricted portions abutting against said primary bosses and extending laterally therefrom along a generally arcuate path in substantially flush fashion in order to provide camming surfaces for inserting said lamp into a socket.

4. A double end contact bayonet type base for electric lamps comprising a cylindrical metal shell, means on said shell for indexing said base in a socket, a plastic web closing the bottom end thereof, a pair of primary bosses projecting from the outer surface of said web and displaced from the center thereof, contacts mounted and exposed on the outer surfaces of said primary bosses, and a pair of secondary bosses projecting from said web and each having a constricted portion abutting against one of said primary bosses and extending laterally therefrom along a generally arcuate path to provide camming surfaces for inserting said lamp into a socket.

5. A base for electric lamps comprising a cylindrical metal shell having an open end for accommodating a glass bulb, means on said shell for indexing said base in a socket, a plastic web closing the other end of said shell, primary bosses projecting from the outer surface of said web and displaced from the center thereof, eyelet contacts mounted on said primary bosses and secured thereto by an outward flange about a central hole through said eyelets, and secondary bosses projecting from said web, each of said secondary bosses having a constricted portion abutting against one of said primary bosses, and extend ing laterally therefrom along an arcuate path in substantially flush fashion and providing a camming surface for inserting said lamp into a socket.

6. A bayonet-type base for electric lamps comprising a cylindrical metal shell having one end open for accommodating a glass bulb, means on said shell for indexing said base in a socket, a plastic web closing the other end of said shell, primary bosses projecting from the outer surface of said web and displaced from the center thereof, contact eyelets mounted on said primary bosses, said primary bosses being substantially cylindrical in shape and having a diameter slightly larger than the diameter of said eyelets at the plane of contact therewith, and secondary bosses projecting from said web, each of said secondary bosses having a constricted portion abutting against one of said primary bosses, said secondary bosses having their outer surfaces flush with the outer surfaces of said eyelets and being extended laterally from said primary bosses along an arcuate path in order to provide substantially flat surfaces adapted to cam the contacts of a bayonet-type plural end contact socket during insertion and rotation of the base therein.

7. A double contact bayonet-type base for electric lamps comprising a cylindrical metal shell having an open end for accommodating a glass bulb, radial pins on said shell for indexing said base in a socket, a plastic web closing the other end of said shell, a pair of primary bosses projecting from the outer surface of said web and displaced from the center thereof, contact eyelets mounted on said primary bosses, said primary bosses being substantially cylindrical in shape and having a diameter slightly larger than the diameter of said eyelets at the plane of contact therewith, and secondary bosses projecting from said web, said secondary bosses being substantially tearshaped and symmetrically disposed between the primary bosses, and each having a constricted portion abutting against one of said primary bosses, said secondary bosses having their outer surfaces flush with the outer surfaces of said eyelets and being extended laterally therefrom along an arcuate path in order to provide substantially flat surfaces adapted to cam the contacts of a bayonet type double contact socket during insertion and rotation of the base therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,185,981 Haller Jan. 2, 1940 2,407,621 Weber Sept. 10, 1946 2,415,867 Cartun Feb. 18, 1947 FOREIGN PATENTS 6,456 Great Britain of 1905 213,383 Great Britain Apr. 3, 1924 

